The electronic encyclopedia that records Pokémon species is called the Pokédex.
In the video games, the Pokédex is a device that stores information about Pokémon encountered or caught by the player. Its entries typically include a species name, number, type, height, weight, and a short description.
The concept was designed as part of the original Pokémon games, where completing the Pokédex gave collecting a clear long-term goal. Professor Oak provides the device to the player in the Generation I story, linking exploration with scientific cataloguing.
The Pokédex should not be confused with a Pokégear, PokéNav, or Pokétch. Those devices provide communication, navigation, maps, or other utilities in particular games. The Pokédex’s defining purpose is identifying and documenting Pokémon species.